Tides

Working along the Cornish coast means I have to be aware of when the high and low tides are each day to get my job done, but for many tides are a thing they know happen but don’t understand and some people aren’t aware that the ocean moves at all.

Knowing the basics about the tides is important if you are going to be around the ocean. Especially if you want to enjoy ocean-related activities – you can’t go rock pooling at high tide!

A simple explanation of the tides

Tides refer to the rise and fall of the ocean which is caused by the interactions between the moon, sun and earth. Generally, most coastal areas have two high and low tides a day.

There are 4 stages of tides:

1. Sea level rises gradually over several hours – flood tide
2. The water level is at its highest level – high tide
3. Sea level falls gradually over several hours – ebb tide
4. The sea level stops falling, reaching its lowest level – low tide

But what causes tides?

The short answer is that the moon’s gravitypulls the ocean towards it. But in fact, what generates tides is the combined gravitational pull of the sun and moon on the earth. The gravitational pull of the moon and the earth’s daily rotation cause the tides to go in and out, the gravitational pull of the moon and the sun combined with their position compared to the earth, causes the tidal range to vary throughout the month, causing the highest high tide and lowest low tide. 

How?

The moon’s gravity pulls the ocean towards it causing a bulge, (lunar tide/high tide) on the side of the earth closest to the moon.

This causes a ‘squeeze’ on the earth and pushes the ocean into another bulge on the opposite side of the earth.

The suns gravity also affects the tides, although much weaker than the effects of the moon, when both are in line with the earth (when a full moon or new moon occurs) their combined gravity cause very high tides (spring tides) and very low tides (neap tides).

It is important to be aware of tides when around the ocean; flood tides can be fast-moving and cut you off quickly if you aren’t paying attention, and the tide going out can be deadly if in the water at the wrong place and time. Always check your tides before heading to the sea – a quick google search ‘high tide’ and the beach you’re visiting.

Tide tables

A tide table is essential for low-tide exploration. If you’re planning activities that depend on a low tide, it is wise to be sure of when the low tide is. But what is a tide table?

A tide table is a handy tool that outlines a particular area’s dates, times and tide predictions. Tide tables are used to determine when the tide changes and when it will be at its very lowest and very highest, helping you find the best tidal conditions for your favourite water activity. 

A typical page from a tide table:

Find the right date

Once you know what activity you want to undertake, pick your date and look for it on the appropriate tide table. 

Determine high tide

If you want to get out in or on the water for wild swimming, boating or kayaking, you will want to know how high the tide will be at its highest and at what time. High tide predicts how high above chart datum, the average of low tide heights for the area, the tide will be at its biggest swell. Look at what time low and high tides will occur, remembering that in most places, the low and high tides are semi-diurnal and occur twice daily. In an area that experiences high tides twice a day, it generally takes about 6 hours for the tide to recede from high to low completely. 

You want to organise your visit around the low tide for rock pooling. It’s worth arriving well before low tide, following the tide out, allowing you the maximum time to explore the lower shore and affording the opportunity to observe marine life as it retreats into hiding. Take care to avoid getting carried away and too distracted discovering various Rockpool species not to notice the tide rushing in on the returning tide. Be careful to stay ahead of the incoming tide and be wary, as gullies can fill in quickly. Allow plenty of time to return to the high beach before the tide comes rushing in. 

Time and tide wait for no man. William Shakespeare 1606

Don’t forget to check the weather alongside the tide chart; weather can influence the height of the waves. For example, high wind can cause waves to rise by more than a foot.